1. Field of the Invention
The present invention relates to an apparatus or a method for forming a film used in manufacturing an EL (electroluminescence) element having a structure composed of an anode, a cathode, and sandwiching between the anode and the cathode a light emitting material, in particular a self-luminescing organic material (hereafter referred to as an organic EL material), from which EL (Electro Luminescence) is obtained.
2. Description of the Related Art
There are two types of EL display devices, a passive (a simple matrix), and an active (an active matrix), and development of both is being enthusiastically performed. In particular, active matrix EL display devices are in the spotlight at present. Furthermore, organic materials and inorganic materials exist for an EL material which becomes a light emitting layer of an EL element, and in addition organic materials are divided into low molecular weight (monomer) organic EL materials and high molecular weight (polymer) organic EL materials. Both are being vigorously researched, but a film of a low molecular weight organic EL material is mainly formed by evaporation, while a film of a high polymer organic EL material is mainly formed by application.
In order to manufacture a color display EL display device, it is necessary to form films of EL materials which emit different colors, for each pixel. However, in general EL materials are weak with respect to water and oxygen, and patterning by photolithography cannot be performed. It is therefore necessary to form the films at the same time as patterning.
The most general method is a method for forming a mask, made from a metallic plate or a glass plate and having an open portion formed in it, between the substrate onto which a film is formed and an evaporation source. In this case, the vaporized EL material from the evaporation source passes through only the open portion to thereby form the film selectively, and therefore it is possible to form an EL layer in which film formation and patterning are performed simultaneously.
With a conventional evaporation apparatus, the EL material which flies off in a radial shape from one evaporation source accumulates on a substrate, forming a thin film, and therefore, considering the distance that the EL material covers, a way of substrate positioning was devised. For example, a method of fixing a substrate to a circular cone shaped substrate holder, making the distances from the evaporation source to the substrate all equal, is performed.
However, when employing a multi-beveling process in which a plurality of panels are manufactured on a large size substrate, the substrate holder becomes extremely large if the above stated process is performed, and this leads to the main body of the film formation apparatus becoming large. Further, the substrate is planar when performing by single wafer processing as well, and therefore the distances from the evaporation source differs within the surface of the substrate, and a problem remains in that it is difficult to deposit at a uniform film thickness.
In addition, if the distance between the evaporation source and the shadow mask is not made longer when using a large size substrate, the vaporized EL material does not sufficiently spread, and it becomes difficult to form a uniform thin film over the entire substrate surface. Maintaining this distance also encourages making the apparatus large size.